1. Field of Invention
Valuable chlorinated hydrocarbons such as ethyl chloride, 1,1-dichloroethane, methylchloroform, and analogous chlorinated derivatives of higher hydrocarbons such as propane or butane are commonly made by liquid phase catalytic hydrochlorination of the corresponding unsaturated precursor such as ethylene, vinyl chloride or vinylidene chloride. Ferric chloride is usually used as the catalyst in such processes. However, the separation of ferric iron from chlorinated hydrocarbons has been a long-standing problem. The presence of ferric iron, particularly in the form of ferric chloride catalyst, during the flashing and recovery of the desired chlorinated hydrocarbons causes dehydrochlorination of the chlorinated hydrocarbons such as methylchloroform and subsequent polymerization of the resulting unsaturated product. Many methods have been tried for removal, deactivation and/or disposal of ferric chloride, but all have serious deficiencies.
2. State of the Art
The most obvious method of removing ferric chloride from chlorinated hydrocarbon streams is the extraction of the ferric chloride with aqueous acid solutions. The ferric chloride is unexpectedly difficult to remove in this manner. Part of the ferric chloride apparently retains some solubility in the organic layer by forming complexes with polymeric material. Furthermore, the resulting chlorinated hydrocarbon product must be dried, which is an expensive procedure on an industrial scale.
Ferric chloride has also been separated from methylchloroform by using almost anhydrous bases, such as the hydroxides of sodium, potassium, and calcium, to absorb the ferric chloride. These materials are relatively inefficient and allow easy pluggage of absorption equipment by the ferric hydroxide produced. The spent bases would constitute a difficult disposal problem. Such a separation process is described in Japanese Pat. No. 71 16,491.
German Pat. No. 1,235,878 discloses a process in which ammonia is used to precipitate ferric chloride. The ammonia is thereafter separated from the chlorinated hydrocarbon product by distillation. Ammonia has also been used in conjunction with steam to precipitate the ferric chloride while removing the chlorinated hydrocarbons by steam distillation (see U.S. Pat. No. 3,115,528). However, the use of these ammonia methods can introduce small amounts of amines as contaminants into the product. Amines or excess ammonia would be at least as undesirable as water. Moreover, steam distillation can aggravate the hydrolysis of a chlorocarbon such as methylchloroform, which is known to occur with great facility in the presence of ferric chloride and moisture.
Ferric chloride has also been removed from chlorinated hydrocarbons by sequestration of the ferric iron by a lower alkanol solution of a partial amide of ethylenediaminetetraacetic acid. Such a process is taught in U.S. Pat. No. 3,848,005. However, this process was intended primarily for the deactivation of small amounts of iron during distillation and thus would not be economical or practical for removal of the relatively large amounts of hydrochlorination catalyst.
Ferric chloride has also been removed from chlorinated hydrocarbons by contacting the chlorinated hydrocarbon streams with activated charcoal and with other porous adsorbents such as silica gel, alumina, or molecular sieves. See, for example, British Pat. No. 1,380,497 and Japanese Patent No. 72 16,801. The adsorbents, particularly activated carbon, work well in removing the iron chloride but contain water which is released to the chlorinated hydrocarbon with the concomitant undesirable effects. Moreover, regeneration of these adsorbents presents problems in corrosion and disposal, since the adsorbed iron has to be removed with an aqueous acid.
The removal of ferric chloride from chlorinated solvents has also been attempted by reduction of the ferric chloride to ferrous chloride through treatment with reducing agents such as stannous chloride, cuprous chloride, or iron, followed by distillation of the solvent, as described in U.S.S.R. Pat. No. 530,877. The use of stannous chloride or cuprous chloride presents an increased expense, and the use of iron creates an increase in the amount of ferrous chloride requiring disposal.
In U.S. Pat. No. 4,001,345 the use of quaternary ammonium salts has been proposed to inhibit the catalytic effects of ferric chloride on methylchloroform during distillation. However, because quaternary ammonium compounds are expensive, the operational cost of such a process would be high. In addition, decomposition of the quaternary ammonium salts to amines may take place.
Other prior art of interest includes the references cited in parent application Ser. No. 122,040 filed Feb. 19, 1980, now U.S. Pat. No. 4,307,261, including especially U.S. Pat. Nos. 3,265,748 (Hurt), 3,420,749 (Dehn) and 3,654,093 (Schexnayder et al), and Kovacic et al, J.A.C.S. 81, 3261-3 (195).
U.S. Pat. No. 3,654,093 relates essentially to the prevention of coke formation in non-catalytic chlorination processes or in any event in processes wherein the process liquids contain only a very small concentration of iron, e.g., iron that becomes a contaminant in the process liquids as a result of their contact with equipment surfaces. As shown in this reference, the process liquids in such cases typically contain only about 0.0004% iron, and the removal of such iron is not addressed as a problem nor solved by the reference. The reference discloses the expedient of adding an alkyl aromatic hydrocarbon to chlorinated hydrocarbons in a very small proportion, e.g., less than 1%, for the purpose of reducing coking or degradation of the desired alkyl chloride product to unwanted polychlorides and other undetermined byproducts during distillation, and subsequently discarding such heavy ends including the hydrocarbon that was added as an anti-fouling agent. By contrast, the present invention deals with the problem of ridding desired chlorocarbons of potentially troublesome residual ferric chloride catalysts, which is present in such chlorocarbons in a concentration of at least 0.01%, by adding to the iron-containing chlorocarbon mixture a reactive, relatively high-boiling hydrocarbon oil in a proportion of at least about 10 volume percent. In this process, ferric chloride is reduced by reaction with the added hydrocarbon while the latter becomes dehydrogenated and converted to a free-flowing carbon-containing powder composed essentially of ferrous chloride. As a result, decomposition of valuable chlorocarbon product is minimized and a powderlike residue is produced that can be easily and safely disposed of.
U.S. Pat. No. 3,265,748 relates to a process for making ethyl chloride by the hydrochlorination of ethylene in the presence of ferric chloride catalyst and seeks to minimize unwanted side reactions such as olefin polymerization and the concomitant build-up of chlorine-containing polymeric catalyst poisons in the system. It achieves this by a special piping arrangement that permits a "disposal liquid" to be continuously purged from the system. However, no hydrocarbon oil is added and no portion of the disposal liquid is recycled in this prior art process, which is essentially a once-through process. As a result, economically important amounts of chlorine and hydrocarbon are lost. In contrast to the instantly claimed invention, the reference totally lacks in teaching an addition of any kind of high-boiling hydrocarbon oil as a medium that is instrumental in preventing any significant decomposition of desired chlorocarbon product by deactivating ferric chloride catalyst residues and removing them from the process in the form of a filtrable, environmentally safe and convenient powder.
U.S. Pat. No. 3,420,749 relates to a distillation process for purifying iron-contaminated hydrocarbon chlorides using at least one mole per mole of iron of an ester of phosphoric or phosphorous acid as a medium for forming a soluble complex iron ester, which is ultimately discarded as part of an unwanted liquid bottoms stream. While this may reduce equipment fouling in the system, it still manifestly allows substantial degradation of desired chlorocarbons and formation of unwanted high-boiling chlorides to take place. In the end, this not only results in a substantial loss of chlorocarbon product and costly ester additive, but actually aggravates the ultimate pollution problem rather than alleviating it.
The Kovacic et al paper describes a purely academic investigation of the reaction of ferric chloride with alkane, without any suggestion of its practical utility and without any particular attention to the kind of residue formed or its ultimate disposal. It totally lacks any disclosure dealing with the manufacture or processing of aliphatic chlorocarbons, much less with the problem of their degradation when they are distilled in the presence of ferric chloride or the possibility of counteracting such degradation by the addition of any other material.
Experience has shown that the disposal of ferric chloride-containing material from hydrochlorination processes poses a constant series of problems in commercial practice. A considerable amount of chlorinated hydrocarbon remains with the ferric chloride-containing material after conventional separation, making it highly corrosive. In addition, flasher fouling has caused a considerable amount of shut-down time. Moreover, increasingly stringent regulations for the disposal of hazardous landfill material have caused an increased impetus to find a more acceptable method for removing and disposing of ferric iron in hydrochlorination processes.
Thus, it is an object of the present invention to provide a process for the removal of ferric iron from hydrochlorination processes whereby the removal of ferric iron is accomplished without substantial decomposition of the chlorinated hydrocarbon product.
It is also an object of the present invention to provide a process for the removal of ferric iron from hydrochlorination processes in which fouling of the hydrochlorination apparatus is substantially reduced.
It is also an object of the present invention to provide a process for the removal of ferric iron from chlorinated hydrocarbons wherein no moisture is introduced into the system.
It is another object of the present invention to provide a low-cost process for the removal of ferric iron from chlorinated hydrocarbons, using a relatively high-boiling hydrocarbon oil as a medium in which dissolved ferric chloride is converted into a filtrable, granular precipitate.
It is still another object of the present invention to provide a process for the removal of ferric iron from hydrochlorination processes whereby the handling properties of the residues are improved.
It is a further object of the present invention to provide a process for the removal of ferric iron from hydrochlorination processes whereby the iron-containing residues are rendered non-hazardous in order to allow ordinary landfill disposal in compliance with environmental protection laws and regulations.
These and other objects, as well as the use of the invention in attaining them, will become more fully apparent from the description which follows.